21 Organs consist of cells and tissues that have been adapted to perform a specific function in living organisms. The stomach is a muscular organ that is located on the left side of the upper abdomen. The stomach secretes acid and enzymes that help in the digestion of food. In simple terms, the stomach is a digestive sac. Even though the stomach has an important role in food digestion, it cannot perform the process all on its own. It depends on other organs such as the salivary glands, esophagus, liver, and intestines to help complete the process. Each organ has its own specific job, but together they make up an organ system. An organ system is a group of organs that work together to perform one or more functions. Which of the following describes the role of the immune system in the body? A. It gets rid of wastes that the body produces. B. It uses electrical signals to control body functions. C. It uses chemical messages to control body functions. D. It gets rid of pathogens that invade the body.​